A cable fault can be caused by an insulation breakdown. The failure modes of such a cable fault can include a short circuit to ground and/or a “soft fault” with a relatively low electrical impedance (or resistance), comparing to that of the cable insulation, between the cable and the earth ground.
For example, in the case of the airfield lighting system, where each lighting segment may contain an array of 250 or more runway light assemblies coupled in series by a power cable buried in the runway which runs as much as 15 Kilometers or more, a power cable fault can lead to a large number of runway lights to go off, resulting in safety hazard and potentially part of the airport runways being shut down. In some examples, a fault or damaged runway light assembly can require a user to replace the runway light or other components of the runway light assembly.
As can be seen, there is a need for an effective safety mechanism to protect a user replacing a runway light or other components of the runway light assembly. For example, a faulty open lamp can cause the voltage of the runway light assembly to a dangerous level to the user.